1. Field of the Application
The present invention relates to foundry practice, and more particularly to the mass production process of making directionally solidifying cast pieces such as, for example, blades for gas turbines or permanent magnets.
2. Description of the Prior Art
For example, there are known methods for producing directionally solidifying cast pieces from a melt, comprising the steps of heating a foundry mould to a temperature exceeding the melting temperature of a metal, melting down the metal, pouring the molten metal into the foundry mould cavity, and cooling the foundry mould by way of bringing it in contact with the cooled surface of a mould (cf. U.S. Pat. No. 3,008,855 and U.S. Pat. No. 2,951,272).
There is also known a method for producing directionally solidifying cast pieces in movable foundry moulds and an apparatus for effecting same, disclosed in British Pat. No. 1,269,833.
The invention of the patent referred to above provides an apparatus formed with a single-piece rotatable bottom plate with foundry moulds being fixedly mounted over the circumference thereof and conveyed through the zone of crystallization. Arranged in the crystallization zone is a heater creating a heat front diminishing in the travelling direction of the foundry moulds. To enable forced cooling of the foundry moulds rigidly mounted on the rotatable bottom plate, a flow of coolant is supplied to the sections of the bottom plate in contact with the lower end portions of said moulds. Such apparatus construction is disadvantageous in that the foundry mould cannot be heated throughout its surface area to a temperature above the melting temperature of metal; the bottom portion of the foundry mould is always underheated while remaining in constant contact with the cooled surface of the mould. Therefore, a more simple process combining metal melting and pouring operations with the heating of a foundry mould is impossible to carry out, since it requires overheating the molten metal to the temperature substantially above the heating temperature of the foundry mould. This procedure, however, is difficult to carry out in the foundry mould as the latter is concurrently subjected to heating.
The above-mentioned apparatus construction suffers from another disadvantage which lies in that by permitting the casting to be produced in the crystallization zone of a definite height or still smaller than that, the furnace production efficiency will be impaired due to shorter length of heat front actively participating in the crystallization process.
Another disadvantage of the aforesaid apparatus construction lies in that the conveyer transportation of the foundry moulds rigidly fixed on the rotatable bottom plate considerably complicates the process and construction of a unit intended for the sluicing of foundry moulds in the event of carrying out the method for the production of directionally solidifying cast pieces under vacuum which is absolutely necessary in the production of gas turbine blades made of highly oxidizable alloys.
It is therefore an object of the invention to provide a method for producing directionally solidifying cast pieces, which will permit the production efficiency to be enhanced and castings to be continuously produced with high quality of structure and improved mechanical properties.
Another object of the invention is to provide a method for producing cast pieces, which will permit the crystallization process to be regulated in a manner to enable the production of castings having various shapes and dimensions.
Still another object of the invention is to provide an apparatus for carrying into effect the method for producing directionally solidifying cast pieces, which is simple in construction and reliable in operation.
Another object of the invention is to provide an apparatus for producing directionally solidifying cast pieces, which is readily applicable in a mechanized or fully automated production process.
An object of the invention is to provide an apparatus of the type described above, which is suitable for operation under conditions permitting control over the temperature and time interval parameters of the production process, making it possible to attain a maximum production efficiency per unit of the bottom plate surface area.